I put in 1 3*Assassin Bomber and it hung doing the animation with the glowing and the edge effect racing around but no menu items work.
This was after I tested it with 5 common souls which gave me 4 Sands of Time which is worth even less than the gold you get for selling them.
I realize this is a bug report but most people don't check that section and should know ahead of time before they drop in all their stored souls trying to get high tier rewards.